Subcutaneous injection is a standard method for the delivery of medication. To facilitate frequent or continuous subcutaneous injection of medication, subcutaneous injection ports are often used. Such injection ports extend through the skin and may remain in place for several days. Currently a major application of such injection ports is to provide chronic delivery of medication such as insulin from portable pumps. When used with a pump, a fluid line is required to connect the injection port to the portable pump. Another application of a subcutaneous injection port is to permit multiple injections without the need to repuncture the skin. In this application, medication is injected from a standard hypodermic syringe and needle through a soft elastomer septum into the injection port which delivers the medication subcutaneously.
If a hollow metal needle is left in place through the skin to provide medication delivery, after one or two days the needle becomes uncomfortable to the patient. To solve this problem, a disposable injection port was described in U.S. Pat. No. 3,547,119 by Hall et al which has a soft, thin-walled cannula which is subcutaneously inserted over a metal needle. After insertion, the metal needle is removed leaving only the soft cannula through the skin. However the Hall invention has several limitations, namely:
(1) it is designed for infusion into the bladder and not for subcutaneous injection;
(2) the soft, thin-walled cannula which is subcutaneously inserted over the metal needle is placed in compression during insertion which can result in buckling of the cannula;
(3) the device has an extremely high profile making it impractical for ambulatory use where it is highly desirable to be hidden under clothing; and
(4) it does not provide a bacterial filter.
More recently, a soft cannula subcutaneous injection set described in U.S. Pat. No. 4,755,173 by Kanopka et al has become available. While being lower in profile than the Hall device and specifically designed for subcutaneous delivery of medication, the Kanopka invention also has several shortcomings, namely:
(1) there is no method for disconnecting the tubing near the point of subcutaneous insertion, thus requiring a long length of tubing to remain connected while showering, exercising or performing other activities for which having a long length of tubing is disadvantageous;
(2) many separate parts are required to construct the injection set which increases costs and the probability of leakage;
(3) like the Hall device, the soft, thin-walled cannula which is subcutaneously inserted over a hollow needle is placed in compression during insertion which can result in buckling of the cannula;
(4) the multiple parts design results in a comparatively high outward protrusion from the skin;
(5) there is a fluid chamber within the device which is a dead space for medication; and
(6) the cylindrical segment of the catheter hub which extends below the holding pad presses on the skin and often becomes uncomfortable for the patient.
Another soft cannula subcutaneous injection port is described in U.S. Pat. No. 4,531,937 by Yates. The Yates device, however, has several disadvantages, namely:
(1) it requires a fluid trapping capability in the needle hub for the expulsion of air from the inside of the device;
(2) like the inventions by Hall and Kanopka, the soft, thin-walled cannula which is subcutaneously inserted over a hollow needle is placed in compression during insertion which can result in buckling of the cannula;
(3) it has a "stepped bore" diameter which forms a fluid chamber within the device which is a dead space for medication;
(4) it does not provide a bacterial filter; and
(5) it lacks a flat surface for attachment to the skin to prevent bending of the soft cannula during prolonged insertion.
Still another soft cannula injection port is described in U.S. Pat. No. 4,311,137 by Gerard. The Gerard device, however, has several disadvantages, namely:
(1) it requires a complex movable needle/septum assembly with one position for flushing and a second position for insertion;
(2) it has a lumen (referred to as a passage) which forms a fluid chamber within the device which is a dead space for medication;
(3) it does not provide a bacterial filter;
(4) the Gerard design results in a comparatively high outward protrusion from the skin; and
(5) like the inventions by Hall, Kanopka, and Yates, the soft, thin-walled cannula which is subcutaneously inserted over a hollow needle is placed in compression during insertion which can result in buckling of the cannula.